This proposal is to seek support to supplement a funded grant to establish collaboration between Dr.Hsieh of Taiwan and the principal investigator. The research of this investigator is built on his proposal " Modeling the HIV Epidemic " which is currently funded by NIH for three years from August 1,1993 through July 31,1996. Specifically this proposal has four specific aims: (l) To develop mathematical models to describe the transmission dynamics which occur in some Asian countries, (2) to develop stochastic models of the HIV epidemic by heterosexual transmission and to explore applications of these models, (3) to characterize HIV infection through heterosexual transmission as well as through other avenues, (4) to develop new methods for estimating unknown parameters incorporating the dynamics of the HIV epidemic and involving population models. Specific aims 1 and 2 will involve a population of prostitutes and a two- sex formulation to account for heterosexual transmission which is the primary mode of transmission in some Asian countries. We will use these models to identify key variables and mechanisms which may contribute to the rapid growth of the HIV epidemic. By using these models, we will also assess impacts of some screening/treatment programs on the HIV epidemic. Specific aim 4 will introduce a new method -the EMM method to estimate unknown parameters. This new method will incorporate the dynamic aspect of the HIV epidemic into estimates of unknown parameters. In this proposal,Dr.Hsieh of Taiwan will be responsible mainly for projects in (D1) whereas Dr. Tan will be responsible mainly for projects in (D2)-(D3). Both Dr. Hsieh and Dr.Tan will be responsible for projects in (D4).